The present invention relates in general to a coin mechanism with a piezoelectric film sensor.
Low average power consumption is desirable in various coin-operated devices such as pay telephones, vending machines and parking meters. Such devices typically include a coin mechanism for determining whether an inserted coin or token is genuine and for determining the denomination of the inserted coin or token. While the coin mechanism must be ready for use at all times, the coin mechanism can consume a significant amount of power when not in use. Moreover, where a battery or other low power source serves as the primary source of power, the continual power drain reduces the lifetime of the power source, thereby increasing the frequency at which the power source must be replaced.
A number of techniques have been devised to reduce the electrical power consumption of coin-operated devices. For example, U.S. Pat. No. 4,733,766, assigned to the assignee of the present invention, discloses a technique for leaving electrical power-consuming aspects of a coin checking apparatus unpowered when the apparatus is not being used. A piezoelectric ceramic element is arranged such that insertion of a coin into the apparatus stresses the piezoelectric ceramic element and produces a corresponding voltage. As explained in the foregoing patent, vibrations that occur upon impact of the coin with a snubber placed in the coin path stress the ceramic material sufficiently to generate the output voltage. The piezoelectric ceramic element can, therefore, be used to sense the arrival of the coin, and the generated voltage can be used to switch on the power of the apparatus.
While the use of piezoelectric ceramic sensors in coin mechanisms has been reasonably successful, several difficulties can arise. First, vibrations caused by events other than insertion of a coin into the coin mechanism can cause the piezoelectric ceramic sensor to generate a voltage and switch on the power. Switching on the power of the coin mechanism under such circumstances is, of course, undesirable. Second, the mechanical mounting of the piezoelectric ceramic sensor in the coin mechanism sometimes requires the use of an adhesive such as glue. Such mounting techniques can affect the mechanical-to-electrical energy conversion of the ceramic sensor, making the determination of whether power should be turned on more difficult. Third, some of the piezoelectric ceramic materials are sensitive to high temperatures. The properties of the ceramic can be degraded during soldering or other high temperature processes if proper care is not taken to protect the ceramic from damage. Additionally, the output signal generated by the piezoelectric ceramic sensor often requires the use of a front end amplifier circuit to provide a sufficiently high signal level. Such circuitry increases the overall cost of the coin mechanism and can increase the power consumption of the unit.
Accordingly, it is desirable to improve the techniques for sensing the insertion of a coin in a coin mechanism and to reduce the overall power consumption of such mechanisms.